Continuous-current generator



1,635,000 'r. c.- LENNOX v I CONTINUOUS CURRENT GENERATOR Filed A g. 20.1925 I s sums-sheen /7 Thomas C. Lennox,

His Attorney.

July 5,1927. 1,635,000

TKO. LENNOX CONTINUOUS CURRENT GENERATOR Filed Auz. 20. 1925 3sums-sheet 2 Durect Current Lmea 20 Inventor: Thomas C. Lennox,

by, His Attor'neg.

July 5.- 1927.

Filed Aug. 20. 1925 3 Shoots-Sheet 3 Fig.7

Inventor: T homas C. Lennox,

by MW His Attorney.

Patented July 5, 1927.

' UNITED STA T lasj' PATENT OFFICE.

THOMAS C. LENNOX, OF PIT'ISIIELD, MASSACHUSETTS, ASSIGNOR TO GENERALELEC- TRIO COMPANY, A CORPORATION OF NEW YORK.

CONTINUOUS-CURRENT GENERATOR.

Application filed August 20, 1925. Serial No. 51,491.

My invention relates to apparatus for generating high voltage directcurrents.

The usual form of direct current generator is limited as regards thevoltage which it can produc'eby reasonof the fact that the coils duringcommutation. This necessitates the use of high resistance conductors inthe current collection circuit and limits the voltage of the individualcoils or phases to small values, and further requires the generation ofalternating voltages which deviate from a sign wave in order that zeroor little voltage exlsts during the period at which the coil may beshort circuited.

- According to my invention I rectify the alternating currents generatedin the coils of a usual type of substantially sign wave armature bymeanswhich permit of completely opening the circuit between the alter-Znating current generator coil and the direct current collecting brushduring the period of reversal, and at the, same time I provide means ofdrawing current from a pluralityof phases without permitting ashort-circuit from phase to phase. This is accomplished by opposing thephase voltages through a circuit containing an auxiliary generator whichgives alternating voltages suflicient to oppose the difference involtage between the phases being rectified and of the proper phaserelation to prevent the flow of shortcircuit current between suchphases. By this means I provide apparatus suitable for delivering directcurrent of substantially uniform voltage and at voltages above that"practicable to obtain with existing apparatus.

The features of my invention which are believed to be novel andpatentable will be pointed out in the claim appended hereto. For abetter understanding of the invention reference is made in the followingdescription to the accompanying drawing in which Fig. 1 represents theessentials of the invention involvin main and auxiliary generators; Fig.2 s ows a modification where the series field of the apparatus is placedin the auxiliary generator; Fig. 3 shows a modification which employs a6-phase main generator; Fig. 4 shows a 12-phase main generator; Fig. 5shows the main generator connected diametrically instead of in ring;.

Fig. 6 shows a method of eliminating one brush circuit; Figs. 7 and 8are curves to be a frequency to the direct current lines 20. It 1 acrossthe posite pairs of these lea s are connected to rectifying devicescomprising segments 13 and brushes 14 having circuits such that they areconnected alternately to the terminals of a transformer having threewindings 15',

16 and 17. It will be observed that each of the two rectifying devicesis arranged so that each phase rectifying circuit is opened completelywhen its terminals are reversed so that no short-circuit occurs .betweenadjacent commutator segments, and that at other times each of the phasesof the winding from which current is being delivered is connected to theterminals of a transformer winding 15 or 16. It will.be observed thatthe positive brushes of each rectifier are connected across onetransformer winding 15 and the negative brushes of each rectifier areconnected across another transformer winding 16. The direct currentlines 20 are connected to the middle points of these transformerwindings.

The third winding 17 of the transformer is shown in two groups connectedto a second synchronous generator 18 arran ed to (ice liver single phasecurrent of of the main generator. This onnection mounted on the sameshaft as the main generator or otherwise kept in exact phase relationgenerator has a shunt field 19 for The main generator has two sets offield coils, one, 21, wound for shunt connection for series connectionin the line' 20. In order to avoid complicating the drawings theconnections between the afield coils and line 20 have been omittedexcept in Fig. 9. The phase rotation between main and auxiliarygenerators and their relative phase posi- 've the desired rer. The mainor ouble the with it and the apparatus is arranged to be I driven by amotor or prime mover notshown.

direct current line 20 and one 22 I tions at any given instant must ofcourse shunt field 21 will cause the generation of an alternatingvoltage in winding 11 which will reach its maximum in each phase at thetime when the rectifier connected to that phase is in contact and halfway between its two open circuit positions. The series field 21 willcause the generation of an alternating voltage in quadrature with thatdue to the shunt field. These field coils need not necessarily be placed011 salient poles as shown in the drawing but may, if desired, bedistributed windings.

The operation of the device is as follows:

The open circuit rectifiers rectify the diametral two phase voltages andapply the resulting pulsating voltages to the terminals of thetransformer windings 15 and 16. Thus, in Fig. 7 if A and B represent thediametral voltages of the generator, voltage pulsations such asindicated by dotted lines a and b will be applied to the transformer.One series of pulsations such as a will appear between the right handlead of 16 and the left hand lead of 15 and the other 6 will appearbetween the right hand lead of 15 and the left hand lead of 16. As thesetwo series of pulsations are not in the same phase position, there willexist unbalanced voltages in the loop or circuit through 13, 14, 15 and1G, and the generator windings at times when all rectifier brushes arein contact, which voltage will tend to set up short circuit currentsthrough the loop so formed. This voltage which is equal to the resultantof A and B during the time when both commutators are active will beapplied half to 15 and half to 16. This total voltage is represented bythe solid lines 0 in Fig. 7. The voltage of the auxiliary generator isrepresented also by c in Fig. 7, except that it is unbroken as indicatedby the dotted lines. It may now be seen how this auxiliary generatorvoltage, although almost exactly of sine wave form, opposes the shortcircuit voltages between commutator brushes and prevents the circulationof short circuit currents. Moreover, due to the uninterrupted nature ofthe voltage of the auxiliary generator, the brushes will come intocontact without substantial difierence in potential between them and therectifier segment they approach.

The direct current lines 20 being connected to the middle points of thetransformer windings 15 and 16 will have be tween them the averagerectifier voltage of the two phases which will be substantially uniformcontinuous voltage. If desired a reactor R may be inserted in the directcurrent line to amp out ripples.

If a load current is drawn from the device it must flow alternately fromthe two rectifying devices and will consequently exist in the brushcircuits as pulsating currents which vary from zero at open circuit tofull load current when the pther phase is open. This is indicated inFig. 8. The upper line L represents the load current which has aconstant value above the zero line marked 0. The wavy line A representsthe current in one brush varying from zero to full value. The currentinthe other brush of like polarity will be of the same form but will reachits maximum when the first is zero as represented by curve 13.

It will be observed that these currents may be considered as consistingof alternating currents imposed on a direct current of half line currentvalue represented by the line 0', and that these alternating currentsflow through the circuits made by the transformer windings, the brushes,and the generator windings with which the brushes are in contact. Ifexcessive induction in the transformer core is to be avoided, thesealternating currents must be opposed by an equal and opposite current.This latter current is supplied by the auxiliary generator We thus havean alternating current of double frequency flowing through a circuitconsisting of the main generator winding 11, rectifiers. transformerwindings 15, 1G and 17. and auxiliary generator 18. This current willnot flow unless an alternating voltage is provided to overcome thereactance of the circuit. This voltage is provided by the series field22 of the main generator. If this field is properly adjusted in relationto line current, it will increase the generated voltage in the maingenerator and advance its phase position sufliciently to disturb thebalance in voltage between main and au. ;iliary generators and set upthe required alternating current in the circuits such that the currentin each rectifying device will be zero in value as its contacts open.

Variations of the scheme are shown in Figs. 2 to 6.

In Fig. 2 the series field 2 is represented as placed in tl i auxiliarygenerator rather than in the main generator.

In Fig. 3, the number of phases in the main generator is increased tosix and the number of rectifiers to three. The auxiliary generator andtransformer are three-phase double frequency. The series field 22 isrepresented in the auxiliary generator 18 but may, if desired, be placedin the main generator.

In Fig. 4 the number of phases of the main generator is increased totwelve with two rectifying devices. An auxiliary generator (not shown)of six times the frequency of the main generator will be necessary here.

In Fig. 5 the main generator is shown arranged for two phases withdiametric connection to the rectifying devices in place of ringconnection. In this case a three-wire direct current system may be hadby connecting the middle wire to the neutral point the transformer hasbeen omitted and the to balance undirectional fluxes.

direct current generator .win ings. This latter feature can be used-withan of the above schemes, if the necessary num er of windings are rovidedin the auxiliary generator an a proper magnetic balance is maintainedamong them.

Fig. 9 shows a modification in which series fields are provided in boththe main and auxiliary generators, and in which the field of the maingenerator is made the rotor element of the machine. In this fi ure 10and 18 respectively represent the mam and auxiliary genera-tors. Thephases of generator are not interconnected in the generator itself butthe windings 15' and 16' of the three phase transformer areinterconnected as shown. The three-phase transformers may be connectedzigzag as shown If desired transformers may be provided between the maingenerator and the rectifiers in case the voltage is very high. The shuntfield 19 ofthe auxiliary generator and the shunt field 21 of the maingenerator are connected across the direct current line 20 through anysuitable type of re ulating device represented at 25- so that t e twofieldswill be fadjusted proportionately. Likewise the series fields 22of the auxiliary generator and the series fields 22 of the main eneratorare connected in series relation with the direct current line 20 throu ha regulating device 26 such that the regu ation willbe proportional. Theauxiliary generator has twice the number of oles as the main generatorto provide the ouble frequenc he provision of series fieldsin both t emain and assed through the auxiliary the main auxiliary generators willgive a somewhat better voltage and current balance in the system thanwhere the series excitation is all provided on one machine. The samescheme may be applied to all the arrangements.

A number of other combinations of numbers of phases and rectifiers ispossible but are not shown as the rinciples involved are the same.' Onerefinement of. design consists of adjusting the waveforms of the twogenerators to such characteristics as will give an exact balance betweenthem and thus minimize the circulation of alternating currents ofharmonic frequencies in the circuits or the imposition of harmonicvoltages on the direct current lines.

In accordance with the provisions of the patent statutes, I havedescribed the princi-v ple of operation of m invention, to ether withthe apparatus whlch I now consi er to re resent the best embodimentthereof; but I esire to have it understood that the appa ratus shown anddescribed is onl illustra tive and that the invention may out by othermeans. I

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is 2-- Apparatus for producing direct currents comprising apolyphase alternating current generator, mechanical rectifiers connectedetween the different phases of said generator and a direct current line,said rectifiers being arranged to completely open the circuit betweentheir direct and alternating contacts at the point of reversal of thewave being rectified, an auxiliary alternating current generator driveninsynchronism with said polyphase generator and rectifiers arranged andconnected to oppose the voltage between rectifiers, said generatorhaving shunt and series fields in quadrature supplied from the directcurrent line.

' In witness whereof, I.have hereunto set my hand this 11th day ofAugust, 1925.

THOMAS C. LENNOX.

carried zo

